German Patent Publication (DE) 3,732,754, corresponding to U.S. Pat. No. 4,885,826 (Strudel) describes such an expander.
At the beginning of the treatment process the circular expander is adjusted to its minimal diameter, that means the staying arms or struts extend essentially parallel to the longitudinal axis of the expander, and the textile tubular fabric is lead over the whole expander so that the expander is inside the textile tubular fabric.
As the expanding control for adjusting the expander width is switched on, the staying arms are expanded outwardly at an angle to the longitudinal axial direction, whereby the staying arms are extended and the tubular fabric is expanded to form the tube.
The spreading of the expander takes place in a relatively short time. Experiments of the Applicant have shown, that because of the resulting increase in volume of the tubular fabric, caused by the spreading of the staying arms, a strong reduced pressure is generated in the interior of the tubular fabric. This reduced pressure causes, on the one hand, that the spreading has to occur against the force caused by the reduced pressure and, on the other hand, a danger exists, that the tubular fabric could be deformed radially inwardly between the staying arms, whereby the tubular fabric could be damaged.